Background: Preterm infants are predisposed to gastroesophageal reflux, which may manifest itself in many ways ranging from failure to thrive to vomiting. Extended distal esophageal pH monitoring is the gold standard for diagnosing reflux in the preterm infants and it is our objective to establish extended distal esophageal pH norms (reference values) for well, asymptomatic preterm infants and to compare with norms already established for term infants, children, adolescents, and adults. Methods: Twenty-one well, asymptomatic preterm infants consuming at least 70% of required maintenance oral feedings were recruited. The mean ± standard deviation birth weight was 1549 ± 439 g (range, 670-2470 g); the mean postconceptional age was 30.7 ± 2.6 weeks (range, 25-35 weeks) and the mean postnatal age was 14 ± 9 days (range, 2-40 days). Extended distal esophageal pH monitoring was performed on each of the infants, and the following parameters were calculated: reflux index, number of reflux episodes per day, number of reflux episodes lasting more than 5 minutes per day, and the longest recorded reflux episode. Results: The mean reflux index was 0.7 ± 1.1%, the mean number of reflux episodes per day was 7.6 ± 11.2, the mean number of reflux episodes lasting more than 5 minutes per day was 0.5 ± 1.1 and the mean longest recorded reflux episode was 4.2 ± 6.1 minutes. These results were comparable to those seen in term infants, children, adolescents, and adults. The trends for pH norms according to postconceptional age and postnatal age seemed to suggest that lower esophageal sphincter maturation might be related to postconceptional age, but the differences observed were not statistically significant (p &gt; 0.05). Conclusion: The norms (reference values) for well, asymptomatic preterm infants were comparable to those seen in term infants, children, adolescents, and adults. With the establishment of these norms, the search for a causal link between many of the respiratory problems encountered in prematurity and gastroesophageal reflux may be aided and the complications associated with gastroesophageal reflux may consequently be reduced.